1. Field of the Invention
The present invention relates to a process for recovering boron trifluoride of a catalyst component from an oligomerization mixture containing olefin oligomers.
2. Description of the Prior Art
An oligomer of olefin with 6-14 carbon atoms is mainly used as a base oil for synthetic lubricant. Among others, an oligomer of linear .alpha.- olefin with 10 carbon atoms has good properties as lubricant. Thus, many processes for manufacturing it have been developed recently.
Known as one of the process for manufacturing this olefin oligomer is a method for oligomerizing an olefin with 6-14 carbon atoms in the presence of a catalyst consisting of boron trifluoride and a complex of boron trifluoride and cocatalyst. In this process, after oligomerization, the catalyst contained in an oligomerization mixture is deactivated by neutralizing the mixture with alkali solution, etc. However, as no catalyst has been recovered, lots of waste materials containing fluorine compounds and boron compounds are produced, requiring the post-treatment thereof after oligomerization.
Many processes have been proposed for recovering the catalyst contained in an oligomerization mixture. One of them is a two-step process comprising separating either boron trifluoride or a complex of boron trifluoride and coatalyst and thereafter separating the other (Japanese Laid-Open Patent Hei 2-108638). This process is advantageous inthat olefin oligomers produced cannot be deteriorated, because either of the two catalyst components has separated first to decrease the activity of the catalyst. This process is advantageous in that no corrosion is caused in the recovery treatment since it is carried out at relatively low temperature. This process, however, has a drawback that it requires a complicated apparatus for recovering the catalyst.
Known as another process, proposed is a process for recovering boron trifluoride which comprises heating an oligomerization mixture at or above a decomposition temperature of a complex consisting of boron trifluoride and cocatalyst to decompose the complex into boron trifluoride and cocatalyst, and thereafter recovering the boron trifluoride (Japanese Laid-Open Patent Hei 2-108638). In contrast to the, foregoing process, this process has an an advantage that it does not require any complicated apparatus. In this process, however, a composition of olefin oligomer tends to change during the recovery treatment of boron trifluoride. Moreover, with this process, boron trifluoride is apt to decompose and the purity of recovered boron trifluoride is lowered, leaving a problem that the boron triflouride recovered can hardly be reused as an olefin oligomerization catalyst as such.
In order to solve these drawbacks accompanying the above methods, the present inventors have found that elevating a temperature of an oligomerization mixture to 110.degree.-155.degree. C. in a short time prevents a composition of olefin oligomer from changing and does not cause the decrease in the purity of boron trifluoride recovered. A patent application for this method has already been filed (Japanese Patent Application Hei 4-221205). However, this process has a drawback that the corrosion atmosphere is so severe at the relatively high temperature that a recovery reactor cannot be used for a long period of time.